High-quality axion from chain seesaw

Abstract

We propose a chain seesaw mechanism to generate not only the masses of neutral neutrinos but also the masses of charged fermions, by supplementing the standard model $SU(3)_c^{}\times SU(2)_L^{}\times U(1)_Y^{}$ gauge symmetries with an additional $U(1)_{Y'}^{}$ gauge symmetry. The chains for the down-type and up-type quarks contain different numbers of links, because the corresponding mediator vector-like fermions and new Higgs scalars carry different $U(1)_{Y'}^{}$ charges. The Peccei-Quinn global symmetry is automatically embedded in this $U(1)_{Y'}^{} $ gauge symmetry which is sufficient to guarantee the high quality of axion.